Effect of Al co-doping on the phase transition of V-doped ZrO2

In this study, V-doped, Al-doped, (Al,V)-doped, and pure ZrO2 powders were prepared using a complex polymerization method, and the thermally decomposed products were characterized using powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). After calcination at 500 °C in air, several small broad peaks were observed in the XRD patterns of all samples. As the heating temperature increased, the phase-transition behavior of ZrO2 varied among the four samples. The phase transition from tetragonal to monoclinic ZrO2 was enhanced in ZrO2 doped with V, but suppressed in ZrO2 doped with Al. The tetragonal phase (t-ZrO2) was dominant in the sample co-doped with Al and V and in Al-doped ZrO2 samples calcined at 700 °C and below, and no diffraction peaks associated with the monoclinic phase (m-ZrO2) were observed. However, after calcination at 800 °C, the diffraction peaks of t-ZrO2 disappeared, and a single phase of m-ZrO2 was observed. SEM observations revealed that the V-doped ZrO2 particles were composed of fine particles in the range of 20–30 nm. In contrast, the SEM images of the (Al,V)-doped ZrO2 powder indicated an increase in agglomerate size compared with that without Al doping. However, elemental analysis using energy-dispersive X-ray spectroscopy (EDX) showed no agglomeration or segregation of Al or V.